1. Field of the Invention
The present invention relates to an engine control apparatus which quickly performs a throttle response operation in an engine idle stop/start (hereinafter also called an “ISS”) period and shortens an engine restart time.
2. Background Art
In the related art, there is known a technology that shortens a start time by increasing a driving torque of a starter motor in order to shorten a restart time of an idle stop vehicle engine or by setting a throttle opening during restart of an engine to an opening side rather than a throttle opening during a typical idle operation in order to reduce inhalation resistance (pumping loss) caused by a throttle valve installed in an intake pipe.
For example, an engine intake control device disclosed in Patent Document 1 is so configured that the throttle opening during engine start is set to a first opening which is larger than the throttle opening during an idle operation to start cranking, and after finishing a first compression process, the throttle opening is set to a second opening that is smaller than the first throttle opening to perform cranking.
According to the device in the related art disclosed in Patent Document 1, the inhalation resistance during the engine start is set to be decreased to reduce a first climbing torque, and the compression resistance in a cylinder in a compression process is set to be decreased to reduce an average cranking torque, so that the starter motor or a battery can be miniaturized.
Also, an engine control device for a vehicle disclosed in Patent Document 2 is so configured that, in a vehicle engine having an electronic control throttle system that opens/closes a throttle valve with an electric actuator so that the throttle valve has a target opening according to an operation condition of the engine and an idle stop/restart system that compulsorily stops the idle operation of the engine when the vehicle is stopped and makes the vehicle start by restarting the engine through driving of a motor with an accelerator operation after the stop, the electronic control throttle system is configured to control the opening of the throttle valve by driving a lever connected to a valve shaft of the throttle valve by the electric actuator. Meanwhile, the electronic control throttle system includes opening setting means at restart, which connects two springs to both sides of the lever and sets the opening position of the throttle valve during power off of the electronic control throttle system to the opening for supplying air flow that is required to restart the engine to the engine in a position in which the urging of the two springs is balanced, and power shutoff means for turning off the power of the electronic control throttle system after the lapse of a set time by gradually reducing the opening of the throttle valve after the compulsory stop of the engine.
According to the device in the related art disclosed in Patent Document 2, the power of the electronic control throttle system is turned off to set the opening of the throttle valve to the opening that is required to mechanically restart the engine after the lapse of the set time after the idle operation is compulsorily stopped at the vehicle stop, fuel injection restarts together with the cranking through driving of the motor to restart the engine if a restart condition is satisfied through accelerator operation, and control is performed to make the opening of the throttle valve after complete expansion gradually close to the target opening according to the accelerator operation. Accordingly, over-discharge of a battery in an engine stop state is prevented, and the fuel efficiency is improved.
Also, a throttle control device of an internal-combustion engine disclosed in Patent Document 3 is configured to change control gains according to an operation state of a throttle valve, so that variation of throttle opening that occurs just after the change of the control gains is suppressed to constantly maintain a stable operation of the internal-combustion engine.
According to the device in the related art disclosed in Patent Document 3, in a device for feedback-controlling a DC motor for opening/closing a valve so that deviation between a sensor value that is an actual opening of the throttle valve and a command value that is a target opening becomes “0”, if the deviation is within a predetermined range (±2°), a normal state is determined, while if not, a transient state is determined, and the control gains (proportional gain Kp and an integral gain Ki) to be used for the respective states are changed, so that responsiveness and stability for control are both established. Also, in the case where the normal state is determined, the control gains are gradually changed to prevent the throttle opening from overshooting from the command value, whereas in the case where the transient state is determined, the control gains are rapidly changed to secure the responsiveness in the transient state.    Patent Document 1: JP-A-2009-127550    Patent Document 2: Japanese Patent No. 3978959    Patent Document 3: JP-A-10-47135
In the case of restarting the engine in the idle stop/start period by using the engine intake control device in the related art disclosed in Patent Document 1, the throttle opening during the engine restart is set to the first opening which is larger than the throttle opening during the idle operation as the target opening value, and an operation amount that is output to the throttle actuator by the throttle opening feedback control operation is calculated. In this case, even if the operation state of the engine is changed, the operation amount (supply voltage to the motor) of the throttle actuator is the same. However, if the temperature of the motor coil is high in comparison to the low temperature state, the resistance value of the motor coil becomes large, and thus the current value that flows through the motor becomes small to lower the motor driving torque. Because of this, the delay of the throttle operation response to the position of the first opening that is larger than the throttle opening during the idle operation becomes large, and thus the time for reaching the opening position, in which the inhalation resistance (the pumping loss becomes small in reverse proportion to the throttle opening value) is lowered by the delay of the throttle operation response, is lengthened. Accordingly, the inhalation resistance reduction effect is not rapidly obtained, and the engine restart time is lengthened (a period from time T1 to time T3 in FIG. 7 to be described later).
Also, in the case of performing the engine restart in the idle stop/start period, a method of waiting for the start while maintaining in advance the throttle valve in a completely open position, in which the inhalation resistance (pumping loss) is low in a period before the engine restarts, may be considered. However, in the case of using the engine control device in the related art disclosed in Patent Document 2, the power of the electronic control throttle system is turned off in the idle stop period, and the throttle valve is maintained in an intermediate opening position in which the throttle valve is mechanically fixed by the urging of the two springs. Because of this, the engine restart is performed by the opening feedback control of the throttle valve from the intermediate opening position to the completely open position in which the inhalation resistance (pumping loss) is low. However, since the resistance value of the motor coil becomes large in the case where the temperature of the motor coil is high in comparison to the low temperature state as described above, the current value that flows through the motor becomes small to lower the motor driving torque, and the time for reaching the completely open throttle position, in which the inhalation resistance is low due to the throttle operation response delay, is lengthened, so that the inhalation resistance reduction effect is not rapidly obtained, and the engine restart time is lengthened.
Further, in the case of performing the engine restart in the idle stop/start (ISS) period by using the throttle control device of the internal-combustion engine in the related art disclosed in Patent Document 3, the throttle opening state before the restart command is the state where the actual opening usually coincides with the target opening within the predetermined opening deviation range (±2°), and the control gain has been changed to the proportional gain in the normal state. If the throttle target opening is set to the throttle opening position in which the inhalation resistance (pumping loss) is low by the restart command, the opening deviation is out of the predetermined range (±2°), and the control gain is changed to the proportional gain in the transient state (the proportional gain value that is larger than the proportional gain value in the normal state according to a third aspect of the invention). However, in the case where the proportional gain in the transient state is set to be large with respect to the proportional gain in the normal state in order to achieve a rapid throttle opening operation response during the engine restart in a throttle actuator operation state in which the ISS is performed after the engine warm-up and it is difficult to achieve the motor current flow (it is difficult to achieve a high motor torque) in a state in which the motor coil has a high temperature, overshoot or undershoot is easily generated when the actual opening converges to the target opening in the throttle actuator operation state in which the motor current flows easily (the motor torque is easily increased) in a state in which the motor coil has a low temperature such as engine start at low temperature.
Accordingly, since there is a possibility that a throttle opening hunting occurs as the opening deviation is varied in the neighborhood of the predetermined range (±2°) and the proportional gain is changed from the proportional gain in the transient state to the proportional gain in the normal state and then to the proportional gain in the transient state, it is difficult to set the proportional gain value in the transient state to be larger than the proportional gain value in the normal state in consideration of the stability of the opening control, and it is usual to adapt the proportional gain so that the stability and responsiveness of the throttle opening control are both established within the operation temperature range of the throttle actuator.
Because of this, in the throttle actuator operation state in which it is difficult to make the motor current flow (it is difficult to achieve a high motor torque) in the high temperature state of the motor coil, such as the ISS execution, the gain marginal value of the proportional gain value that is set with respect to the proportional gain value at which the throttle opening hunting occurs is excessively set. Accordingly, in the operation state in which the motor coil temperature becomes high such as the ISS execution, the resistance value of the motor coil becomes large to make the motor current flow difficult, and thus the motor torque is lowered. Accordingly, the delay of the throttle operation response occurs to lengthen the time for reaching the completely open throttle position, in which the inhalation resistance is low, and thus the inhalation resistance reduction effect is not rapidly obtained to lengthen the engine restart time.
As described above, if the motor temperature is changed due to the engine operation state and the resistance value of the motor coil is changed in the case where the proportional gain is fixed with respect to the operation temperature of the throttle actuator, the motor current value is not the same even if the motor control voltage value is the same. Because of this, when the same opening deviation (=the target opening−the actual opening) occurs, although the control duty value and the motor control voltage value, which are calculated by the PID control operation, are controlled to be the same value, the motor current value is changed due to the change of the resistance value of the motor coil that is caused by the motor temperature, and thus the motor driving torque that is in proportion to the motor current is not controlled to be the same value. That is, the motor driving torque that is controlled and output when the same opening deviation occurs becomes high at low temperature and becomes low at high temperature.
Accordingly, since the gain of the motor control system is heightened as the temperature is lowered, it is usual to adapt the control gain so that the control hunting does not occur at low temperature. In this case, as illustrated in FIGS. 4A and 4B, since the gain of the motor control system is deteriorated due to the increase of the motor coil resistance value in a high-temperature operation state, the torque that is required to drive the throttle valve is not output straightly, and the actual opening response is delayed (see FIG. 4A). Also, if the control gain is adapted to obtain the rapid valve driving at high temperature, the gain becomes excessive at low temperature and thus the hunting of the actual opening occurs (see FIG. 4B). Because of this, it is usually required to adapt the PID control gain so as to avoid the opening hunting at low temperature while sacrificing the opening responsiveness during the high-temperature operation. At this time, as illustrated in FIG. 4, L denotes a target value, M denotes a control amount response at low temperature, and N denotes a control amount response at high temperature.